Magnetic switch



Aug. 29, 1950 H. L. BRousE- 2,520,525

MAGNETIC SWITCH v Filed April 1, 1948 w Hum illllll IN V EN TOR. A AAOZOZ. 6200::

Patented Aug. 29, 1950 2,520,525 FF 1 CE MAGNETIC swi'ron HaroldL.Brouse, Cincinnati, Ohio, assignor, by mesne assignments, to RobotAppliances, Inc., Detroit, Mich, a corporation of Michigan ApplicationApril 1, 1948, Serial No. 18,378

3 Claims. (Cl. 200112) Another object of the invention is the provisionof a switch of the magnetic type especially adapted for underground use.

A further object of the invention is to provide a hermetically sealedmagnetically operated switch suitably adapted for use under extremeconditions of temperature and humidity.

A still further object of this invention is to provide a mercury switchso constructed that the operating efficiency and life expectancy is inno way affected by the presence of the mercury.

Other objects and advantages of the invention will appear upon athorough consideration of the following detailed description composedwith reference to the drawings which constitute a portion of thisspecification and in which:

Fig. 1 is a perspective view of a switch embodying the instantinvention.

Fig. 2 is a front elevation view of the switch with the front coverremoved.

Fig. 3 is a rear elevational view of the switch with both the terminalcover and the asphalt packing removed.

Fig. 4 is a vertical sectional view taken substantially on line 4-4 inFig. 2 with both'covers in place.

In Fig. 1 numeral l0 designates a switch case of non-magnetic andchemically inert conductive material such as stainless steel, having afront cover [2 and a terminal cover l4 provided with an opening NS forthe reception of a dual conductor cable l8. The front cover l2 has anoutwardly deformed central portion 20 coated on the inside surface witha suitable insulating compound 22, such as plastic adhesive, and rolledalong the outer edge thereof into a locking and sealing engagement withthe rim of the case It.

The case In is soldered, or otherwise mounted, on a footed bracket 24having an outstanding annular flange 26 for supporting the terminalcover l4 and providing a case connection terminal 28. The foot of thebracket 24 is welded, or otherwise secured, to a plate 30 so as toprovide a convenient base for mounting the switch in an uprightposition.

An elongated non-magnetic stud 32, of stain- :less "steel or othersuitable conductive material, is

mounted centrally in the rear wall of the casing Ill and fixedly held atsubstantially right angles thereto by a sealing and insulating grommet34, of an inert resilient material such as a type of chlorinatedsynthetic elastomer, That portion of the stud 32 within the casing I0 isprovided with an annular flange 36 seated against the inner face of thegrommet 34 and drilled axially to receive, in a press fit, a non-manetic pin 38,

I 2 of suitable conductive material, having an enlarged retaining headon the free end thereof.

That portion of the stud 32, outside the case I0, is decreased in crosssection to provide an annu larshoulder 39 adjacent the rommet 34 forseating a non-magnetic spacer bushing 40 adapted to imposed apredetermined amount of compression on the resilient rommet 34. Thesmaller portion of the stud 32'is threaded to receive a nut 42 forholding the spacer bushing 40 in seat against the shoulder 39 andproviding lateral support for a central terminal connector 44 locked onthe stud by a retaining nut 46. A bar magnet 48 of high permeabilitymaterial is mounted in a nonmagnetic cradle 50 which is suspendedcentrally from the pin 38 for balanced rotation thereabout withinpredetermined angular limits.

The magnet 48 is bonded in the cradle 50 by a suitable cement andfurther secured therein by means of clips 52 and 54, provided on eitherend of the cradle 50, and turned down over the top of the magnet 48. Thecradle 50 also has a triangular' shaped contact point 56, dependent fromeach end thereof, adapted to make contact with'a pool of suitableconductive liquid 58, such as triple distilled mercury, when the cradleand magnet assembly is rotated a predetermined distance in eitherdirection.

The rotational limits of the cradle assembly are defined by a cushionstop comprising a section of resilient tubing 60, such as rubber, fittedover a laterally extended bracket 62 supported by a downturned footwedged between the rear wall of the case I!) and the inner flange of thegrommet 34.

The cushion stops, by defining the limits of travel in either direction,prevent the cradle assembly from rotating, under the influence of astrong magnetic field, so as to cause the contacts 56 to float invertedon the surface of the mercury pool rather than remain immersed.

This completes a discussion of the structural details of the invention;however, to facilitate a better understanding of the subject matterinvolved, a brief discussion will be directed to the manner in which theswitch is assembled and the way in which 'it'operates to perform itsintended 7 function.

In assembling the switch it is extremely important to remove as muchmoisture as possible from the airwithinthe casing so as to preventoxidation of the parts. This reaction, byway of illustration, will.occur readily at a temperature of F.- and relative humidity of 45percent. However, at this same temperature, the relative humidity mustbe constantly maintained below 15 percent to avoid the possibility ofsuchoxidation.

This undesirable oxidation, as well as mercury pollution, resultfromthe'presence of greases and various soldering -or.,welding fluxespresent on certain of the component parts. It is, therefore, essentialthat the case be washed in boilin ater after soldering so:- as to removeall excess flux It is also advisable to immerse all parts in a suitabledegreasing solution and then adopt measures in assembling the switch toprevent any deposition of greases on either the enclosed working: partsor the surfaces defining theenclosure.

After the working parts of the switch have been. assembled within thecase, the placed; in a dehydrated atmosphere so as to charge the casewith moisture-free air. If it is deemed advisable, the case may becharged with a gas. such as nitrogen or hydrogen so as to reduce furtherthe possibility of corrosion. and chemical activity. Caution must.-alsobe exercised. soas to selectsubstantially chemically inert materialsto. be. used for the fabrication. of those. elements, in theswitch whichare normally exposed eitherto the conductive liquid or its. vaporswhenal chemically active substance like mercury is employed,

Before the front cover I7. is placed on. the case It), however, a thin.coating of a rubber cement is preferably applied to the or matingsurface thereof and permitted to. dry at a temperature slightly abovethe. boiling point of water so as to evaporateany moisture present. i

melted asphalt and forced in. place over the terminals. I Y

The. casing isthusv hermetically sealed,- thereby making the switchespecially well adapted for use in installations which are-constantlysubjected to varying extremes of temperature and moisture. Therefore,barring damage to the. switch caused by impact. or overload, repeatedtests have shown 4 would energize the coil temporarily by means of thecar battery as the vehicle is passing over the underground magneticswitch. This would cause the switch to close so as to complete a circuitfor reference to the details of a single embodiment and: adaptation, itwill be appreciated by those skilled in the art that the principlesinvolved, as well as the device itself, are susceptible ofnumerousother: applications.

Therefore, what I claim and desire to secure by Letters Patent is:

1. A. magnetic switch comprising, an electricall'y conductivenon-magnetic and hermetically sealed case,- a conductive. terminal studhaving a threaded section on one end anda seating flange on. the otherend mountedin one side of the case, insulating means including aresilient grommet sleeved. around the stud and. seated against the studflange, adjustable means for cooperation V with the threaded section to.compress the gromthat the device will function indefinitely without 7any loss in sensitivity or efficiency.

In operationv the switch. is. placed in an position on the base-3flsolthat cradle 50 is free to pivot about the pin 38. Therefore, whenthe magnet 48, carried by the cradle. 53, is exposed to a magnetic fieldof sufficie'nt intensity,

the forces of attraction and repulsion are. citedthe switch, andconsequently any circuit-in which it is connected, until. it is again.caused to close in one direction or another imder the influence of amagnetic field of sumcient intensity as above described.

One use of the switch as contemplated by the applicant, is inconjimction with. automatic: garage door operating equipment. In thisconnec tion, the switch may be installed in the ground beneath adriveway so as to be within the operating range or influence of amagnetic on the under side of an automobile or other'sim'rlar vehicle.In such an installation, the dn'yer met a predetermined amount into asealing engagement with the case, a conductive cradle in the casemounted for limited. rotation. on. the stud a permanent. magnet mountedcentrally infthe cradle, and a pool of conductive liquid in the caseadapted to immerse one end or the. other of. the cradle and magnet.assembly as it rotates in re.- sponse to a magnetic. stimulus.

2. A magnetically operated switch comprising, an. electricallyconductive non-magnetic andhermetically sealedcase, a conductiveterminal stud having a threaded section on one end and a seating flangeon the opposite end. mounted in one wall of the case by adiustable meansincluding a resilient insulating grommet sleeved on the central portionof v the stud and seated on one end against the stud flange, andnon-magnetic for cooperation with the threaded section on the terminalstud to compress the grommet av predetermined amount into a sealingengagement with the case, a. conductive cradle in the case mounted forlimited rotation on the terminal stud, a permanent magnet mountedcentrally in the cradle, and a. pool of conductive liquid: in the caseadapted to immerse one end or the other of. the cradle and magnetassembly as it rotates. in response toa magnetic stimulus.

3. In a magnetic switch having: a sealed case containing an; electricconductin liquid and a conductor member above the level: of. the liquid.

a tiltable. cradle to receive and hold a; bar magnet comprising, anelongated sheet metal base to simport the magnet, a pair of. oppositelydisposed REFERENCES CITED 1 The following references are at record inthe file of this patent? UNITED STATES PATEN'I'S Number Name Date1,975,762 Behmer Oct. 9, 1934 1,992,214 H... Feb. 26, 1935 2,052,9-LlWeathers Sept. 1, 1936 2,240,891 Merchant May c, ion

